Straight course locator for airplanes



May l2, 1953 o. s. FIELD STRAIGHT COURSE LOCATOR FOR AIRPLANES 2Sheets-Sheet l Original Filed Aug. 30, 1945 OOON MDDPCD o. s, Fil-:LD nSTRAIGHT COURSE LOCATOR FOR AIRPLANES May l2,r 1953- 2 Sheets-Sheet 2Urgnal Filed Aug. 30, 1945 mi( E2 mom- S III Gttorneg .Nom

Patented May 12, `l 953 UNITED ST oFFicE STRAIGHT COURSE LOCATOR FORAIEPLANES @scar S. Field, Rochester, N. Y., assigner to General RailwaySignal Company, Rochester, N. Y.

2 Claims.

This invention relates to course finding systems'for airplanes, and moreparticularly pertains to the provision of a straight course indicatorfor use in connection with determining the course of an airplane betweena series ci successvely spaced radio ground stations.

This application is a division of my prior application, Ser. No.613,600, filed August 30, i945, which has resulted in Pat. No.2,599,632, dated May 3Q, 1950, relating; to a block signal system forairplanes; and no claim is intended to be made in this application tosuch a block signalling system, it being understood that the presentinvention as disclosed and claimed herein relates to a course locatingsystem which may at times he employed with such a block signallingsystem and at other times may be used alone,

It has been proposed in the above mentioned parent case to divide atramo route into block sections having a plurality of altitude routesover such trahie route. n the ground alongr such trahie route arelocated suitable radio block stations adapted to cooperate withsignalling apparatus on the airplanes so that the proper trafficcondition is displayed in the cab of each airplane as it flies along thetraiic route through the successive blocks at any one oi the assignedaltitudes. Although such a system may give the desired trafficinformation to the airplanes as they fly over the route, it is alsonecessary that each airplane be able to determine that it is ying alongthe proper course outlined by the block stations. It is of courseunderstood that conventional altimeters may be used to determine thatthe airplane is travelling at the proper altitude. Also, it will beappreciated that automatic direction finding apparatus has thedisadvantage, however, that side winds cause the airplane to drift sothat it actually fails to follow a straight course between successiveblock stations.

In view of the above considerations, it is proposed inv accordance withthe present invention to provide suitable means to cooperate with thesuccessive ground radio stations so as to manifest on an airplanewhether or not it is dying directly over a straight route connecting anypair of such successive ground stations.

It is also an object of the present invention to provide such a systemthat it may cooperate with radio ground stations used merely fordelneating a course, or may also cooperate with ground stations used inconnection with a block signalling system such as disclosed in the abovementicned. parent application.

Other objects, purposes, and characteristic features of the presentinvention will in part be described hereinafer and will in part beunderstood from the accompanying drawings, in which- Fg. l is adiagrammatic view of a succession of block stations with which theapparatus of the present invention may cooperate in locating the routefor an airplane; and

2 illustrates the apparatus employed in a system provided by the presentinvention for indicating to the pilot of an airplane a straight routebetween two successive ground stations irrespective of a substantialtendency of the airplane to drift sideways due to a side Wind.

As described in the above mentioned parent application, it is necessaryin order to manifest the presence of an airplane precisely Within thelimits of a particular block of an air trahie route that the beginningand end of such a block section be rather definitely defined. To dothis, it is proposed in the parent application to provide at thestarting point of each block section a comparatively narrow radio beaconof the fan marker type, such radio beacon being rather Wide transverselyof the air route but rather narrow longitudinally of the airway.Obviously, the end of such block route is manifested by the reception ofradio energy from the fan marker at the beginning of the next blocksection. In addition, other directional radio transmitting facilitiesare provided adjacent each fan marker to transmit the traffic conditionsin connection with each block. However, insofar as the present inventionis concerned the various features of the block system may be ignoredsince the present invention may be used with or Without such a system.All that is necessary in connection with the present invention is thatthe successive block stations be distinctively identifiable.

More specifically, the ground located apparatus has beendiagrammatically illustrated in Fig. 1 asA constituting a radiotransmitter at the entrance end of each block which radiates spaceradiation energy forwardly and upwardly toward an airplane flying inthat block. Likewise, a ground located radio transmitter is located atthe exit end ci each block which radiates space rachation energy towardeach ori-coming airplane in that block. In other words, the airplanecarried apparatus (shown in Fig. 2) requires space radiation energytransmitted thereto from the front and from the rear simultaneously butat different carrier frequencies, and Fig. l has merely indicatedsuicent apparatus to do this. As previously mentioned, this groundapparatus may or may not be a part of a block system.

Fig. 2 illustrates the apparatus in the cab of an airplane AP forindicating whether or not that airplane is flying directly over theroute and if not to what extent it is deviating from` such route. Thisroute flying apparatus of Fig. 2 is, of course, contemplated as beingused in connection with the ground located transmitters illustrated inFig. 1, and also shown and described in detail in the prior parentapplication.

Referring now to Fig. 2, the airplane carried apparatus includes theusual and well known automatic direction finding equipment ADF. Thisinstrument is provided with a directional antenna |14 and a senseantenna |10 and this instrument also includes a pointer |1| which isoperated by its vertical shaft |19 and which will point to the radioground station that emits carrier frequency to which both thedirectional antenna |14 and the sense antenna |10 of this instrument ADFare tuned. The exact construction of this automatic direction findinginstrument is deemed unnecessary because it is well known in the art andfor further description thereof attention is directed to pages 207-219,of Aviation Radio, by Henry W. Roberts, 1945.

In accordance with the invention illustrated in Fig. 2, this automaticdirection nding instrument has physically mounted upon the indicatorshaft |19 thereof a directional antenna |12. This directional antennahas its output wires connected to an amplier |13 which has its outputleads connected to the primary windings and |16 of the transformers Trland Tr2, respectively. This directional antenna |12 is tuned to the samefrequency as is emitted by a ground located radio transmitter located atthe entrance end of the block under consideration, namely, to the rearof the airplane. This airplane carrier apparatus also includes a secondreceiver-amplifier |11 which is fed by energy from a sense antenna |18.This receiver-amplifier |11 is also tuned to the same carrier frequencyas is the directional antenna |12. The sense antenna |18 is, however,omni-directional whereas the antenna |12 is highly directional. Theoutput leads from the receiver-amplifier |11 are connected to theprimary windings |35 and |36 ofthe transformers Trl and Tr2,respectively.

It should fbe observed that the primary windings |85 and |86 areconnected to the output leads of the receiver-amplifier |11 in likefashion; whereas, the windings |15 and |16 of these same transformersare connected to the output leads of the receiver-amplifier |13 inunlike fashion. From this construction, it is readily seen that underthose conditions where the windings |15 and |85 are energizedaccumulatively from the ground station in the rear, this same groundstation will cause energy to flow in the windings |16 and |85 in buckingrelationship, and vice versa. When the airplane under consideration isflying precisely over the route the directional antenna |12, which ispreferably of the circular coil type, is disposed in a plane such thatzero energy is induced therein from the ground located radio transmitterto the rear of the airplane. Under this same circumstance energy will bereceived by the omni-directional antenna |18 so that thereceiver-amplifier |11 delivers energy through its output circuit to theprimary windings |85 and |86 of transformers T1| and Tr2, respectively.

In other words, energy of the same value (zero r4 energy being inducedby primary windings |15 :and |16) is induced in the secondary windings|8| and |82 of the transformers Trl and Tr2, respectively. With likepotentials applied to the grids y of the amplifying tubesTl and T2 likepotentials will also result on the deflecting plates |83 and |84 of thecathode ray viewing tube or cathode ray scope K. With like potentialsapplied lon the two deflecting plates |83 `and |84 the lighted spot iton the cathode ray screen will assume the center position as illustratedin Fig. 2.

If now, on the other hand, the airplane should veer to the left of theroute the directional antenna |12 would no longer receive zero energyfrom the ground located station in the rear so that it would at least toa slight extent render the receiver-amplifier |13 active. This wouldLcause the primary windings |15 and |16 of the transformers Trl and Trto be lightly energized and this energy would in the case of thetransformer Trl subtract from the excitation supplied by the windings|85 so that the output from the transformer Trl would become less;whereas, the output for the transformer '1*12 would become greater thanit was before, due to the fact that the energies applied to the windings|16 and |85 of this transformer TTB are accumulative. *With theamplifying tube T2 passing more current than the amplifier Tl thedeiiecting plate i3d will become less positive than the deflecting plate|83, as a result of which the electron beam in this cathode ray scope Kwill be bent toward the left so that the spot will be located slightlyto the left of the location illustrated in the drawing. Should, however,the airplane veer to the right off of the route over which it is to fly,the phase of the current induced in the directional antenna |12 will beshifted 180 as a result of which the energies applied to the windings|15 and of the transformer Trl will become accumulative and the energiesapplied to the windings |16 and 186 of the transformer Tr2 will becomesubtractive as a result of which the tube Tl will draw more current thanwill tube T2, the deflecting plate |85 will therefore become lesspositive than the defiecting plate |84 and the spot |80 on the screen ofthe cathode ray scope K will be shifted to the right. In other words,the cathode ray scope K will, by the location of its lighted spot |80 onthe screen thereof, inform the pilot whether he is flying to the. leftor to the right of the route over which he is to fly.

With reference to Fig. 1, two airplanes APZ and APS, are shown, eachbeing equipped with the apparatus of Fig. 2 and respectively dying ataltitudes 2000 and 3000. Along the traiic route are located thesuccessive ground stations, such as Fix 1, Fix 2, Fix 3, and so forth.Each such ground station is equipped with directional radio transmittersTAF|| and TAFZS. The transmitter TAFII radiates a distinctive frequencyfl as compared to the frequency f2 radiated by the transmitter TAF 25.

T hese directional antennas are supplied with radio frequency signals inany conventional way so as to radiate continuously radio signals towhich the airplane apparatus may respond. Obviously, such transmittersmay be used without any connection to a block signalling system, or maybe used with suitable controls imposed thereon as described in the aboveidentified parent application.

Having thus described a straight course indipresent invention, it isdesired to be understood that this form is selected to facilitate in thedisclosure of the invention rather than to limit the number of formswhich it may assume; and it is to be further understood that variousmodifications, adaptations, and alternations may be applied to thespecific form shown to meet the requirements of practice, without in anymanner departing from the spirit or scope of the present invention.

What I claim is:

1. An airplane route delineating system having airplane route indicatingapparatus comprising in combination, an automatic direction nder havinga shaft with a first directional antenna rotatedrthereby effective whentunednto the frequency of a ground station in advance of the airplane toalways maintain the shaft rotated so as to direct said antenna towardsaid station in advance, a second directional antenna rotated by saidshaft and directed at right angles to said first directing antenna so asto receive minimum radiated energy from a station in the reartransmitting at a distinctive frequency, said second directional antennabeing effective to receive minimum radiated energy only when the line offiight of the airplane coincides with the straight line distance betweenthe advance and `rear transmitting stations, radio receiving apparatuson the airplane tuned to the frequency of the station in the rear andassociated with said second direction antenna, said radio receivingapparatus having its output variable from maximum to minimum inaccordance with the radiated energy received by said second antenna fromthe station in the rear, other radio receiving means having anomni-directional antenna tuned to the frequency of the station in therear, a cathode ray tube having oppositely disposed deflecting means forgoverning the relative position of a beam on the screen of the tube, atransformer for each of said defiecting means of the cathode ray tube,said transformer having two primary windings, circuit means connectingthe output of said radio receiving apparatus to one of the primarywindings of each of the transformers, said Circuit means connecting theprimary windings of the two transformers oppositely, circuit meansconnecting the output of said other receiving means to the other of theprimary windings of each of the transformers, said circuit means havingthe same phase connections for both transformers, and circuit meansconnecting the outputs of the transformers to their associateddeflecting means respectively.

2. An airplane route delineating system having airplane route indicatingapparatus comprising in combination, an automatic direction nnder havinga shaft with a first directional antenna rotated thereby effective whentuned to the frequency of a ground station in advance of the airplane toalways maintain the shaft rotated so as to direct said antenna towardsaid station in advance, a second directional antenna rotated by saidshaft and directed at right angles to said first directing antenna so asto receive mim'- mum radiated energy from a station in the reartransmitting at a distinctive frequency only when the line of ght of theair plane coincides with the straight line distance between the advanceand rear transmitting stations, radio receiving apparatus on theairplane tuned to the frequency of the station in the rear andassociated with said second direction antenna having its output variablefrom maximum to minimum in accordance with the radiated energy receivedby said second antenna from the station in the rear, other radioreceiving means having an omnidirectional antenna tuned to the frequencyof the station in the rear, a cathode ray tube having oppositelydisposed deflecting means for governing the relative position of a beamon the screen of the tube, and resolving means for combining the outputsof the two receivers in a manner to set up a variable differentialvoltage in said oppositely disposed dei'lecting means, the differentialvoltage being at a minimum only when the output of said first receiveris at a minimum.

OSCAR S. FIELD.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,143,178 Wright Jan. 10, 1939 2,252,063 Cockerell Aug. 12,1941 2,296,041 Luck Sept. 15, 1942 2,364,624 Dugan Dec. 12, 19442,379,362 Lear June 26, 1945 2,490,051 Hardy Dec. 6, 1949

